Inhibition of active strontium transport from erythrocyte ghosts by internal calcium: evidence for a specificity controlling site.

The inhibition of strontium transport from erythrocyte ghosts by internal calcium was investigated. When active strontium transport was measured in the presence of increasing levels of internal calcium it was found that the inhibition of strontium transport started at an internal calcium level of 0.3 mM and was virtually complete when this concentration reached 1.0 mM. It was also noted that calcium transport was virtually constant between concentrations of 0.3 and 1.0 mM. This experiment indicated that calcium did not inhibit strontium transport by competing for the active site of the transport system. This inhibition was partially reversed by increasing the internal magnesium concentration from 1 to 4 mM. A higher level of magnesium at the time of lysis and during incubation enhanced strontium transport. However, the inhibition remained noncompetitive with respect to calcium. Manganese was also found to support calcium and strontium transport. However, it could not reverse the inhibition of strontium transport by internal calcium at any concentration tested. In fact, manganese restored the inhibition of strontium transport by calcium in ghosts that were prepared and incubated in solutions that had high magnesium levels.